This invention concerns toners containing block copolymer charge directors. More specifically it concerns such charge control agents which are preferably quaternized.
Several patents exist in the field of charge directors in toners.
In U.S. Pat. No. 4,355,167 Ciccarelli (1982) there are disclosed certain polymeric charge control agents for electrostatic toner compositions that are random copolymers of the formula [AxBy]z wherein A is a segment selected from vinyl monomers, B is a quaternary salt segment, x and y are numbers representing mole fractions of A and B, the sum of x and y being equal to 1, and Z represents the degree of polymerization. Free radical polymerization techniques are said to result in a telomeric quaternary salt having a number average molecular weight of from about 1,000 to about 10,000.
In U.S. Pat. Nos. 4,371,601 Ciccarelli (1982) and 4,378,419 Ciccarelli (1983) there are disclosed positively charged dry developer compositions containing such polymeric charge control agents.
In U.S. Pat. No. 4,621,039 Ciccarelli et al (1986) there are disclosed related toner compositions with fast admixing characteristics comprising certain polymeric charge control agents for electrostatic toner compositions that are homopolymers of amine-containing monomers, copolymers containing amine monomers, polymeric amines, polymeric quaternary ammonium compounds, telomeric amines and telomeric quaternary ammonium salt compositions, wherein the charge enhancing additives are associated with the pigment particles. An essential disclosure of Patent No. '039 is that the charge agent is associated with the pigment particles. Association was affected by mixing the pigment particles and charge control agent prior to adding the resulting mixture to the polymer resin particles required for formation of the toner composition. This Patent further teaches that it is necessary to disperse the pigment particles within the polymeric resin, and without proper dispersion, charge sharing does not result.
In addition to the advantages of proper dispersion of the pigment particles within the toner resin taught by '039, in some instances, particularly where color pigments are used, proper dispersion of the pigment is also desirable in optimizing color quality in the xerographic image.
U.S. Pat. No. 4,656,226 Hutchins et al (1987) teaches the preparation of AB block copolymers suitable for use as pigment dispersants, by group transfer polymerization techniques (GTP) such as those disclosed in U.S. Pat. Nos. 4,417,034 (1983) and 4,508,880 (1985) both to Webster, and 4,414,372 (1983) and 4,524,196 (1985) both to Farnham et al, and 4,588,795 Dicker et al (1986). Quaternized block copolymers, preferably made by GTP, are disclosed in U.S. Pat. No. 4,755,563 (1988) West.
Quaternary ammonium salts as charge control agents in toners are taught in U.S. Pat. No. 3,893,935 Jadwin et al (1975).
Pressure-fixable toners containing copolymers of styrene and dimethylaminoethylmethacrylate are taught in U.S. Pat. No. 4,581,312 Nakahara et al (1986).
Toners containing block copolymerized styrene and dyes are known from U.S. Pat. No. 4,568,624 Ohshima et al (1986).
The above patents are hereby incorporated herein by reference. They provide relevant background for the present invention, but none suggest ways or means of further improving triboelectric charge and compatibility of charge directors with the toner resin.
There is a need for improved developer compositions which contain toner and carrier particles, wherein the toner particles charge positively. Further, there is a need for developer compositions which can be used to render visible electrostatic latent images containing negative charges on the photoreceptor surface, and which compositions will transfer effectively electrostatically from such a photoreceptor surface to plain bond paper without causing blurring or adversely affecting the quality of the image. Moreover, there is a need to provide charge control agents which are even more compatible with the toner resin, the charge control agent having exceptional dispersibility while exhibiting higher uniform and stable net toner charge. Further, there is a need for charge control agents that facilitate the dispersion of the pigment within the toner resin so that charge exchange is promoted and color quality is optimized.